It is a legal requirement in some countries for lamps used to mark the position of the vehicle at night so as to be visible when the vehicle is observed sideways on.
Several prior art signal lamps are known which perform such a dual-purpose position-marking function.
In particular, CIBIE's published French patent application No. 77 01895 describes a signal lamp in which a single monofilament bulb is associated with a first reflector for creating an axial light beam to mark the position of a vehicle when seen axially. A second reflector is disposed adjacent the inner side of the bulb for reflecting a portion of the light rays emitted by the bulb toward its outer side, i.e. to reflect said portion of light out sideways from the vehicle, thereby serving to mark the position of the vehicle when seen sideways-on. To this end, the catadioptric element which is provided to the side of such a lamp and which would normally constitute an obstacle to the sideways beam is modified in order to pass the beam and to diffuse it.
However, this arrangement suffers from several drawbacks. First, it may be expensive to provide a specially-designed catadioptric element. Secondly, it is necessary for the depth of the axial beam reflector to be reduced in order to avoid interfering with the passage of the sideways beam thereby reducing the intensity and the visibility of the axially-directed light flux emitted by the signal lamp.
Published French patent application No. 2 177 382 describes a vehicle signal lamp comprising a single light source, a first and very small reflector for creating an axial beam (in order to mark the position of the vehicle when seen axially), and a second reflector which is provided to one side on the inner wall of the lamp in order to reflect a portion of the emitted light rays out sideways from the vehicle, thereby marking its position when seen sideways-on. In this case, the side catadioptric element is prevented from constituting an obstacle to the sideways beam by displacing said catadioptric element in the depth direction of the lamp. This type of lamp suffers from a first drawback in that the axially directed beam is of limited intensity because of the very small size of the associated reflector. Secondly the disposition of the component parts of the lamp is such that it necessarily occupies a considerable depth and is therefore completely unsuited to the shallow or low profile lamps currently desired by the market. Finally, this type of lamp requires two distinct reflector elements to be provided, thereby constituting a complicated and expensive structure.
More generally, if a shallow lamp disposed on the corner of a vehicle for providing axially-visible position-indicating light and comprising a relatively deep axial reflector with a laterally-disposed catadioptric element is, in addition, to perform a sideways marking function using light emitted by the same filament as provides the axially-visible light, then it may be necessary not only to provide an additional reflector but also to provide a window through the axial reflector and the catadioptric element, or at least to modify the catadioptric element. There are two main reasons why this is disadvantageous: first, providing a window through the axial reflector gives rise to an undesirable black hole in the projected image of the lamp; and secondly, modifying the catadioptric element or providing a hole therethrough makes it more difficult for the element to satisfy regulations and may also provide a visible discontinuity in the element which is undesirable from the point of view of appearance.
Preferred embodiments of the present invention mitigate the drawbacks of the prior art and provide a vehicle signal lamp which, while remaining relatively shallow, is nevertheless capable of providing highly effective position marking for the vehicle both when seen end-on and when seen sideways-on.